1. Field of the Disclosure
This disclosure relates to a backlight unit, and more particularly to a backlight unit adapted to prevent light leakage caused by a light guide plate of wedge type and a liquid crystal display device having the same.
2. Description of the Related Art
Recently, personal mobile terminals have been rapidly researched and developed. Mobile terminals such as notebook (or lap-top) computers and personal digital assistants (PDAs) have been applied to electronic data processing systems (EDPSs). Moreover, mobile terminals such as cellular phones and navigation systems being of specialized uses have been widely spread.
With the most recent development of electro-communication technologies, the performance of mobile terminals has been rapidly enhanced. For example, cellular phones have been improved so that they can connect to the interne and include a digital camera. As such, the cellular phones can take still and moving pictures and send these pictures by radio. Furthermore, cellular phones are improving enough to be employed for a small-sized database, which makes it possible to manage schedules and edit/store documents.
Such mobile terminals make use of liquid crystal display (LCD) devices which can be provided with superior contrast and color reproduction and manufactured in large quantities, in order to configure a display screen. The LCD devices are widening their application fields as a result of their features, such as their light weight, slimness, low driving voltage, and so on. This trend is evident in the ways in which the LCD devices have been applied to office automation equipment, audio equipment, video equipment, and more.
The LCD device controls a transmitting amount of light on the basis of image signals applied to a plurality of control switches, in order to display a picture. The LCD devices are not self-illuminating display devices. In accordance therewith, an LCD device includes a backlight unit provided on the rear surface of an LCD panel which displays images.
FIG. 1 is a planar view showing an image display portion included in a cellular phone or a mobile terminal of related art. FIG. 2 is a cross-sectional view showing an LCD device included in a cellular phone or a mobile terminal of related art. As shown in FIGS. 1 and 2, a cellular phone or a mobile terminal of the related art includes a display portion 5 configured to display images and a body portion configured to have a key pad and a variety of menu keys which are not shown in the drawings.
The display portion 5 includes a case 15, a small-sized LCD device 8, and a window plate (not shown). The case 15 is formed to have an opening OP which allows images to be viewed through it. The LCD device 8 is disposed into the inner side of the case 15 and displays images to be viewed through the opening OP. The window plate projects the images displayed on the LCD device 8 and protects a display area of the LCD device 8.
The small-sized LCD device 8 included in the cellular phone or the mobile terminal is configured to include an LCD panel 10, a backlight unit 70, a support main 30, and a bottom cover 35. The backlight unit 70 and the support main 30 are disposed under the LCD panel 10. The bottom cover 35 is formed to surround the lower and side surfaces of the support main 30. Such an LCD device 8 is manufactured in a size small enough to be used in the portable cellular phone or the portable mobile terminal. As such, a top case encompassing the edges of the LCD panel 10 is removed from the LCD device 8. The edges of the backlight unit 70 and the LCD panel 10 are encompassed by the support main 30. The bottom cover 35 prevents a breakaway of the backlight unit 70.
The support main 30 is formed in a rectangular rim shape. The support main 30 is provided with at least one light source 45, a reflection sheet 55, a light guide plate 40, and optical sheets 60. At least one light source 45 is disposed on at least one inner sidewall surface of the support main 30. The reflection sheet 55 is disposed on the rear surface of the support main 30. The light guide plate 40 and the optical sheets 60 are sequentially disposed on the reflection sheet 55.
The light source 45 is also disposed parallel to a side surface of the light guide plate 40. The light source 45 is mounted on a first flexible printed circuit board (PCB) 50 which is connected to a backlight driving circuit (not shown). The backlight driving circuit generates a driving signal used for driving the light source 45.
The LCD panel 10 is placed on the backlight unit 70. An edge of the LCD panel 10 is connected to a PCB (not shown) via a second flexible PCB 13. The PCB loads driver circuits. The LCD panel 10 includes a thin film transistor substrate 23 and a color filter substrate 20. The LCD panel 10 further includes polarizing plates 27 and 29 each attached to a lower surface of the thin film transistor substrate 23 and an upper surface of the color filter substrate 20.
The small-sized LCD device 8 uses high-brightness light emission diodes that are smaller and thinner than a fluorescent lamp and configures the light source 45. An edge of the light guide plate 40 adjacent to the light source 45 becomes thickest, and the remaining portion of the light guide plate 40 is formed in a thinner plate shape than the adjacent edge to the light source 45. In other words, the light guide plate 40 is formed in a wedge type (i.e., to have a wedge portion “wgA”).
Such a structure of the light guide plate 40 allows the optical sheets 60 to be disposed on the thin portion of the light guide plate 40. As such, the entire thickness of the LCD device 8 can be reduced.
However, the LCD device 8 with the light guide plate 40 of wedge type causes a light leakage phenomenon which forces the brightness of a part of the image display area AA adjacent to the wedge portion “wgA” of the light guide plate 40 and the light source 45 to become brighter than that of the rest of the image display area. Due to this, the picture quality of the LCD device 8 is deteriorated.